In the case of diesel fuel, in particular in newly industrializing countries and developing countries there is the problem that said fuel contains a large proportion of water, partially owing to intentional admixture, partially owing to poor production and/or storage conditions and technologies. So that the water contained in the diesel fuel does not enter the internal combustion engine, a wide variety of different technologies have become known for precipitating the water out of the diesel fuel. The precipitated water is discharged manually or in an automated fashion depending on the vehicle technology. Double-armature solenoid valves as described, for example, in DE 10 2007 005 916 A1, have become known for the automated discharging of water which is usually under pressure in a water accumulator of the motor vehicle fuel system. The known double-armature solenoid valves have proven themselves, but efforts are being made, in particular with respect to corresponding environmental requirements, to improve further the safety of such double-armature solenoid valves in order to reliably avoid unintentional discharging of fuel, in particular of diesel fuel, into the environment.
In the double solenoid valve which is known from DE 10 2007 005 916 A1, two armatures are arranged with their end sides axially opposite each other along a common adjustment axis and are moved toward one another into a central or respective opening position by energizing a common coil. As a result, an inlet opening, through pressurized water flows, is opened into the armature space, which pressurized water exits the armature space again via the outlet opening. In order to close the two openings, the energization of the coil is interrupted and the two armatures are moved into the respective closed position, i.e. in the direction of the respective opening (inlet opening or outlet opening) by a common restoring spring which is supported with its two axial ends on one of the armatures in each case. According to the teaching of the document, instead of a common compression spring, separate restoring springs which are each embodied as a tension spring can be used. In the known double-armature solenoid valve, after the interruption of the energization of the coil the armatures are moved uniformly into the respective closed position, with the result that the inlet opening and the outlet opening are closed simultaneously.
U.S. Pat. No. 4,778,227, which is from a different specialist field, discloses a double-armature magnet of a brake system. The double-armature solenoid valve comprises two flat armatures which are arranged axially adjacent to coil means and spring force is applied to them axially away from each other, with in each case one spring in the direction of a respective closed position. The spring which applies spring force to the flat armature which is assigned to an inlet opening is configured to be weaker here than the spring which applies spring force to the other flat armature which is assigned to the outlet opening, so that when the energization of the coil means is interrupted the inlet opening is closed more slowly than the outlet opening.